Over-expression of the epidermal growth factor receptor (EGFR), or its ligand TGFα, is frequently associated with breast, lung and head and neck cancer, and is believed to contribute to the malignant growth of these tumors. The development of compounds that inhibit the kinase activity of the EGFR, as well as antibodies that block EGFR activation, for use as anti-tumor agents is an area of intense research effort.
Epidermal growth factor (EGF), acting through its receptor EGFR, is a mitogen and survival factor for normal human keratinocytes as well as other epithelial cells (Rheinwald, J. G. and Green, H., 1977, Nature 265, 421; Rodeck, U. et al., 1997, J. Cell Science 110, 113). Thus, there is the potential that use of EGFR inhibitors in chemotherapy would interfere with the normal renewal of skin and other epithelial tissues such as the cornea and the lining of the gastrointestinal tract: Toxicity to proliferating tissues such as skin and the G1 tract is frequently a dose-limiting side effect of cytotoxic agents. Such toxicity may be manifested, among other symptoms, as a skin rash, diarrhea, corneal thinning, hair atrophy or loss, hair follicle dysplasia, degeneration, necrosis or inflammation, interfollicular epidermal hyperplasia, or a failure to heal or a delayed healing after injury.
Treatment of normal keratinocytes and EGFR over-expressing tumor cells with the EGFR inhibitor, [6,7-bis(2-methoxy-ethoxy)-quinazolin-4-yl]-(3-ethynylphenyl)amine, causes cell cycle arrest, as indicated by an accumulation of cells in the G1 phase of the cell cycle (Moyer et al., 1997, Cancer Res. 57:4838-4848). Progression of cells from the G1 phase into the S phase requires the phosphorylation of the retinoblastoma protein, pRB, which is mediated by cyclin-dependent kinases. Consistent with its ability reduce the percentage of cells in S-phase, we have observed that CP-358,774 causes depletion of hyper-phosphorylated retinoblastoma protein (ppRB) and accumulation of the cyclin-dependent kinase inhibitor, p27kip1/waf1 (Moyer et al., supra).
The keratinocyte growth factor (KGF) family consists of KGF-1 and KGF-2, also known as FGF-7 and FGF-10, respectively, reflecting their homology with proteins, in the fibroblast growth factor superfamily. Various patent publications describe KGFs and their uses, including PCT International Publication WO 94/23032, published Oct. 13, 1994; PCT International Publication WO 98/06844, published Feb. 19, 1998; PCT International Publication WO 98/16243, published Apr. 23, 1998; PCT International Publication WO 98/16642, published Apr. 23, 1998; and PCT International Publication WO 98/24813, published Jun. 11, 1998.
The KGFs are unique among FGFs in that they act exclusively on epithelial cells. Both KGFs are expressed by stromal cells and act as paracrine mediators of epithelial cell proliferation (Finch et al., 1989, Science 245:752; Igarishi et al., 1998, J. Biol. Chem. 273:13230). KGF-1 and KGF-2 are 57% homologous, and both bind to the FGFR1iiib receptor with high affinity (Igarishi et al., 1998, supra; Miceli, R., et al. 1999, J. Pharm. Exp. Ther. 290:464). Since KGFs appear to be paracrine factors in the skin (Marchese, C., et al., 1990, J. Cell Phys. 144:326; Igarashi, M., et al., 1998, supra), we investigated whether the KGF pathway can serve as an alternate means of mitogenic signaling in this tissue, thereby potentially alleviating the epithelial toxicity caused by administration of an EGFR inhibitor.